refactor and remove assert

Author: martijnvg

server/src/main/java/org/elasticsearch/index/mapper/AbstractScriptFieldType.java

@@ -192,7 +192,7 @@ public ValueFetcher valueFetcher(SearchExecutionContext context, String format)
      */
     protected final LeafFactory leafFactory(SearchLookup searchLookup) {
         String include = name();
-        var copy = searchLookup.maybeCopyWithSourceFilter(new SourceFilter(new String[] { include }, new String[0]));
+        var copy = searchLookup.optimizedSourceProvider(new SourceFilter(new String[] { include }, new String[0]));
         return factory.apply(copy);
     }
 

server/src/main/java/org/elasticsearch/search/lookup/ConcurrentSegmentSourceProvider.java

@@ -44,16 +44,12 @@ class ConcurrentSegmentSourceProvider implements SourceProvider {
     }
 
     private ConcurrentSegmentSourceProvider(ConcurrentSegmentSourceProvider source, SourceFilter filter) {
+        assert source.isStoredSource == false;
         this.sourceLoaderProvider = source.sourceLoaderProvider;
         this.isStoredSource = source.isStoredSource;
-        if (isStoredSource) {
-            this.sourceLoader = source.sourceLoader;
-            this.storedFieldLoader = source.storedFieldLoader;
-        } else {
-            this.sourceLoader = source.sourceLoaderProvider.apply(filter);
-            // Also re-initialize stored field loader:
-            this.storedFieldLoader = StoredFieldLoader.create(isStoredSource, sourceLoader.requiredStoredFields(), true);
-        }
+        this.sourceLoader = source.sourceLoaderProvider.apply(filter);
+        // Also re-initialize stored field loader:
+        this.storedFieldLoader = StoredFieldLoader.create(isStoredSource, sourceLoader.requiredStoredFields(), true);
     }
 
     @Override
@@ -77,9 +73,13 @@ public Source getSource(LeafReaderContext ctx, int doc) throws IOException {
     }
 
     @Override
-    public SourceProvider maybeCopyWithSourceFilter(SourceFilter sourceFilter) {
+    public SourceProvider optimizedSourceProvider(SourceFilter sourceFilter) {
         assert leaves.isEmpty() : "source provider must be unused when applying filter";
-        return new ConcurrentSegmentSourceProvider(this, sourceFilter);
+        if (isStoredSource) {
+            return this;
+        } else {
+            return new ConcurrentSegmentSourceProvider(this, sourceFilter);
+        }
     }
 
     private static class Leaf implements SourceProvider {

server/src/main/java/org/elasticsearch/search/lookup/SearchLookup.java

@@ -153,8 +153,8 @@ public Source getSource(LeafReaderContext ctx, int doc) throws IOException {
         return sourceProvider.getSource(ctx, doc);
     }
 
-    public SearchLookup maybeCopyWithSourceFilter(SourceFilter sourceFilter) {
-        SourceProvider copy = sourceProvider.maybeCopyWithSourceFilter(sourceFilter);
+    public SearchLookup optimizedSourceProvider(SourceFilter sourceFilter) {
+        SourceProvider copy = sourceProvider.optimizedSourceProvider(sourceFilter);
         return new SearchLookup(this, copy);
     }
 }

server/src/main/java/org/elasticsearch/search/lookup/SourceProvider.java

@@ -37,8 +37,16 @@ static SourceProvider fromLookup(MappingLookup lookup, SourceFilter filter, Sour
         return new ConcurrentSegmentSourceProvider(lookup, filter, metrics);
     }
 
-    default SourceProvider maybeCopyWithSourceFilter(SourceFilter sourceFilter) {
-        assert false : "should not be invoked";
+    /**
+     * Optionally returns a new {@link SourceProvider} that is more optimized to load source with the provided source filter in mind.
+     * <p>
+     * Currently, if source mode is synthetic, and only a subset of fields are requested, then only loading source for requested fields
+     * is much more efficient.
+     *
+     * @param sourceFilter The part of the source caller is actually interested in.
+     * @return a new instance if source can be loaded in optimal a more optimal way, otherwise returns this instance.
+     */
+    default SourceProvider optimizedSourceProvider(SourceFilter sourceFilter) {
         return this;
     }
 }

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plugin/ReinitializingSourceProvider.java

@@ -53,7 +53,7 @@ public Source getSource(LeafReaderContext ctx, int doc) throws IOException {
     }
 
     @Override
-    public SourceProvider maybeCopyWithSourceFilter(SourceFilter sourceFilter) {
+    public SourceProvider optimizedSourceProvider(SourceFilter sourceFilter) {
         assert perThreadProvider == null : "source provider must be unused when applying filter";
         return new ReinitializingSourceProvider(sourceFilter, sourceProviderFactory);
     }